This history of multimedia presentation in the classroom begins with the cart containing a projector, for example, 16 mm film projector, slide projector or overhead projector. The cart is generally rolled in by a member of the audiovisual staff and used by the teacher. The film, slides, or material to be displayed within the room is generally secured separately by the teacher. Thus there is a scheduling requirement in obtaining the material and the projector at the same time. Similarly, the ability of the teacher to use the equipment varies. The transport and use of the equipment produces unnecessary wear and tear on the equipment, as well as the medium to be loaded and viewed. Although initially television sets were also provided on carts, most classrooms today are equipped with permanent television sets.
The next level of development was the including of cable connections to each of the classrooms either from a cable tv service (CATV) or a master antenna (MATV) as in the home or in hotel or motel rooms. The teacher then had available programming which was scheduled by the supplier of the CATV or MATV service. This requires the teacher to schedule the presentation about the schedule of the service provider.
Early attempts to provide a central location within a facility having a plurality of multimedia devices, each assigned to a specific channel on a cable wire service, has not been cost effective. To match the quality of signal produced by the cable company, the equipment required in the facility include, high quality broad band amplifiers, automatic audio/video level equipment with separate sync and video processing to maintain the correct AM picture modulation level, circuits to reduce the sound to match the cable company's sound carrier reduction scheme, top quality band pass filters for each channel, high quality AGC, etc. To provide an RF signal of less than cable quality is unacceptable and causes more problems.
Dynacom has provided systems which include individual cables connecting monitors in the room with a central location which controls a plurality of multimedia sources so as to selectively provide prearranged multimedia material to the classroom when desired. The controls in the classroom activate and deactivate scheduled materials on que from one of a plurality of sources. Using fiber optics as the communication link between the classrooms and the central location, AM or IM "intensity modulation" for the video with an audio FM subcarrier riding on the AM video do not produce the desired signal. As with the cable system, expensive signal processing equipment would be needed to provide the desired quality of signal. Thus there is a need for fiber transmitters and receivers using a different method of signal transmission.
Also in the earlier systems, a separate routing system was used for the audio and video signals. This greatly increased the expense of the installation. Combining a modulated audio signal as a subcarrier on a modulated video signal as a single input to a routing switch also did not produce acceptable results without expensive signal processing.
Prior art optical transmitters of audio-video signals use a single RF-FM video carrier with the audio channel as a subcarrier on the base band video. In order to transmit and receive a quality signal, expensive additional circuitry and filters were required to obtain acceptable audio signal to noise ratio. Circuitry included complex optical drive and current sensing circuitry which further included complex temperature and bias controls.
In the earlier Dynacom systems, an interface was developed between the systems controller and the source to allow the remote control signals from the classroom to be interpreted and control the multimedia source. Using a VCR for example, interface had to be programmed for converting the remote control signal from the system to the appropriate remote control signals for the specific VCR. The interface device was then hardwired into the internal controls of an off-the-shelf VCR. This requires an extensive amount of time for the conversion and installation of the interface to an off-the-shelf VCR since the appropriate connection points had to be determined for each source. The same problem exists for the monitors in the classroom.